Ultrasound imaging techniques are useful in depicting tissue, such as blood vessels, and its characteristics through the transmission of ultrasound pulses. Such techniques are commonly used in medical procedures because these ultrasound imaging techniques allow physicians to localize and identify various structures, thereby aiding in, for example, the classification of blood vessel types and quantification of blood flow abnormalities. Other example procedures include the insertion of a needle or the placement of a catheter. Current ultrasound imaging techniques include two-dimensional or three-dimensional B-mode, spectral pulsed or continuous wave Doppler, and two-dimensional or three-dimensional color flow mapping.
Ultrasound imaging techniques may employ the Doppler principle on blood flow within vessels, which may provide information such as blood flow direction and blood flow velocity. Such information may be used with known blood vessel characteristics to determine the type and/or location of the blood vessel.
Pulsed wave (PW) Doppler is one type of ultrasound imaging technique used for detecting blood vessels, as well as blood flow direction, velocity, and other vessel characteristics. PW Doppler may be formed by the measurement of Doppler shifts that occur in a transmitted ultrasound pulse sequence, which are caused by the movement of ultrasound scatterers from one pulse to the next. The transmitted pulse sequence may be sinusoidally modulated, for example. The measurement of Doppler shift is taken from a sample volume of the returned echo signals from more that one pulse. A display may illustrate, in a histogram or other format, the sample volume and its corresponding characteristics. A scanner that incorporates the PW Doppler technique may thereby provide a display that enables a user to determine the type and position of a blood vessel located within the sample volume as well as detailed characteristics of the blood flow within the vessel.
It should be noted that, conventionally, the term “Doppler ultrasound” is used in the art to describe techniques for estimating the rate of movement of ultrasound scatters. The Doppler principle, in general, describes the perceived or apparent change in frequency, and/or wavelength of a wave by an observer who is moving relative to the wave's source. The apparent change, known as the Doppler effect, may be caused by a motion of the observer, by a motion of the source, or by both a motion of the observer and the source. With respect to ultrasound technology, the term Doppler originated in the continuous wave systems where it applies reliably.
The actual role of the Doppler effect in pulsed wave (PW) systems, however, has been questioned by some researchers due to other factors inherent in the PW measurement process. For example, Doppler-based systems typically estimate the phase of returned echoes and measure the rate of change of these phase estimates to determine the Doppler shift frequency. Alternatively, in some PW systems several techniques exist for measuring scatterer velocity that rely strictly on time displacement measurements between pulses, instead of phase measurements. In effect, PW systems typically attempt to measure the shift in position of target echo signals to estimate their motion velocity. However, the term “Doppler” still endures, even in such PW situations where the Doppler effect may not actually be a factor in the measurement process.
Conventional ultrasound scanners that assist in determining the location and identification of blood vessels, such as a PW Doppler scanner, may include user controls that require adjustment during the imaging process. Physicians or technicians, in attempting to locate or identify a blood vessel using an ultrasound scanner, may need to adjust a setting on the scanner to obtain a more accurate reading of the vessel or to gather further information related to the reading. Such user interaction can cause a breach of sterility requirements, which are often necessary during medical procedures. Additionally, a conventional ultrasound scanner may have a probe that operates within the sterile field and a main unit that operates outside the sterile field. The main unit may be enclosed in a plastic cover to enable it to be located within the sterile field, but in such cases the physician or other operator may be limited in the adjustments that can be made using the controls of the main unit.
In addition to the sterility issues that arise in connection with the adjustment of scanner controls and settings, conventional ultrasound scanners are generally complex and provide extensive control options for a variety of diagnostic image capabilities. Often, a physician or other user of a scanner may simply need to locate a vessel and determine the size of the vessel.
Thus, there is a need for an ultrasound imaging technique and scanner that identifies blood vessels with a relatively minimal amount of user interaction.